1. Field of the Invention
The present invention relates generally to the conversion of digital data to analog data. More specifically, the present invention relates to the use of digital to analog converters (DACs) to convert digital data to analog signals in recovery systems such as set top cable boxes.
2. Related Art
Currently available set top cable boxes generally include one or more DACs. Each DAC typically includes several clocks to provide timing to various components within the DAC. More particularly, these clocks ensure that the output of audio and/or video data samples is output from the DAC at the same sample rate that data is input to the DAC. For example, the currently available set top cable boxes may include formats based upon moving picture experts group (MPEG) data transport. To ensure proper operation of these MPEG conforming set top cable boxes, resolving timing issues, such as the correlation between input and output sample rates, becomes absolutely critical. Matching input and output sample rates in DACs are desirable in order to prevent overflow or underflow of data within the DAC.
Resolving timing issues is much more difficult in more complex set top cable boxes. Complex set top cable boxes may decode several data streams simultaneously, requiring several different system clocks. For example, one set top box might support two televisions, with each television supporting different programming. Additionally, it is contemplated that each television may be able to support features such as picture-in-picture, such that each television can display two different programs simultaneously. In these examples, each separate data stream associated with each of the separate features will require its own local clock. More specifically, to ensure proper synchronization, each of these local clocks must operate at a clock rate directly related to the input sample rate of its associated data stream. Thus, a single DAC capable of accommodating multiple data streams and multiple set top box features, will require several system clocks.
As set top cable boxes and other audio/video systems that use DACs become even more complicated, miniaturizing DACs and other critical system components becomes a significant design challenge. Thus, from this perspective, a single DAC that requires multiple clocks can impose significant limitations and demands on DAC chip designs with miniaturization requirements.
What is needed therefore is a mechanism to reduce the number of clocks required for a single DAC to accommodate multiple data streams. The multiple data streams are created as a function of complex audio/video programming features that operate at different input sample rates. More specifically, what is needed is a method and system to enable a DAC to use a single clock capable of operating independent of the input sample rate.